1. Technical Field of the Invention
The present invention generally relates to a degassifying apparatus for removing air or other gas from a liquid in which it is dissolved.
2. Discussion of the Prior Art
Many liquids are considered to be undesirable when they contain dissolved gasses, e.g., solvents and chemicals used in such liquid chromatography techniques. As one example, in solvents used in the performance of liquid chromatography techniques, more small dissolved gas bubbles appear as the sensitivity of the detector increases. As a result, highly accurate and precise results cannot be obtained unless such dissolved gas is removed from the liquid. Even extremely small amounts of bubbles, i.e., dissolved gasses, cause noises which are proportional to increases in the sensitivity of the detector. Additionally, the greater the amount of gas dissolved in the liquid, the more quickly chemicals, oils, and other materials having such bubbles will deteriorate. In other words, deterioration of drugs and oils accelerates in proportion to the amount of dissolved gasses, e.g., air, which is present in the liquids.
In order to overcome these problems, it has been conventional to remove dissolved gas from liquid by boiling, decompression or vacuum, or by using an ultrasonic technique. These conventional methods, however, are disadvantageous and suffer from defects because as they fail to sufficiently remove dissolved gas from liquid. Additionally, they can only be used with a limited number of liquids; they are accompanied by dangers; and they cannot be incorporated into a continuous system, e.g., a liquid chromatography system, because they allow degassified and/or deaired liquid to reabsorb air, dependent upon the manner of manipulation of the system. All of these negate the desired aeration effected by the system.
More particularly, the boiling method, which deairs or degassifies liquid by heating and boiling, is dangerous and inapplicable when used with a flammable liquid. This method is inconvenient and disadvantageous because as it cannot be applied to liquids, e.g., organic solvents, which change in quality when heated.
The vacuum or decompression method, which de-airs or degassifies liquid by using an aspirator or a decompression device, suffers from the following inconveniences and/or shortcomings: it requires the use of a water system when an aspirator is used; low boiling point liquids may boil in a vacuum; and liquids may reabsorb air after they are no longer subjected to a vacuum.
Finally, the ultrasonic method, which de-airs or degassifies liquids by exposing the liquids to ultrasonic waves, is also inconvenient and defective because it requires an ultrasonic oscillator and because it must be used jointly with the vacuum method, as a result of its insufficient deairing or degassifying effect.
Other inconveniences and/or shortcomings which are associated with conventional methods of degassification include, e.g., that the methods cannot be incorporated into an integrated system such as liquid chromatography, and, as a result, liquids heated at a different location must be brought into the system. Additionally, there is a risk that the results of a desired treatment or process will be meaningless unless the liquids are handled properly, because the liquids may, at a later time, reabsorb air or other gas when such conventional degassifying methods are used.
One alternative degassification method, as proposed in parent application Ser. No. 258,908, incorporates the use of an elongated synthetic resin tube contained in a deairing enclosure tank, which is maintained in a depressurized condition, i.e., under at least a partial vacuum in order to remove gas dissolved in the liquid which passes through the tube. Such a degassification method is advantageous insofar as it eliminates the disadvantages and defects of the conventional methods noted above. However, this method is disadvantageous insofar as the degassification enclosure tank must have an unduly large size; otherwise, the elongated synthetic resin material would not be efficiently accommodated within the tank; on the other hand, if the tube is positioned too close to the walls of the tank, then the total surface area of the tube which is exposed to the depressurized atmosphere within the tank will be insufficient to attain the desired and required degassification of the liquid in the elongated tube. It is, therefore, desirable to maximize the surface area of the tube exposed to the vacuum conditions in order to enhance degassification.
Additionally, because the deairing or degassification method occurs while liquid is being circulated, connecting elements located between the tube, through which liquid to be deaired is passed, and the enclosure tank in which the tube is positioned, as well as between the tube and an external implement, are often exposed to, and readily corroded by, the liquid to be degassified. As a result, exterior air is readily admitted into the tank via the connecting elements, resulting in failure to efficiently reduce pressure in the tank. Accordingly, it is necessary to utilize a device to prevent such shortcomings.